1. FIELD OF THE INVENTION
The present invention relates to internal combustion engine ignition timing devices, and more particularly to a dynamic direct measurement ignition timing device. Still more particularly, the engine timing device of the present invention is especially adapted for determining piston top dead center for setting and monitoring the ignition on Harley-Davidson motorcycle engines.
2. DESCRIPTION OF THE PRIOR ART
The Harley is an exasperating beast. For something that has been around for so long, there has been remarkably little refinement. One of the hardest things to do properly is to set the ignition timing without an extended trial and error sequence. Top dead center (TDC) and ignition timing are usually marked on the flywheel of the Harley engine. There is an inspection port which can be opened by removing a plug to permit observation of the ignition timing or TDC marks if the conditions are favorable. Unfortunately, oil and dirt permeate the flywheel environment. Even more frustrating, until the 1993 model, the view port and timing marks of a Harley were located on the opposite side of the motorcycle from the position where the ignition unit, which needs to be adjusted for proper timing, is secured to the engine. A mechanic must repeatedly switch from one side of the machine to the other in the trial and error sequence required to set the electronic ignition, ignition breaker points, or to position the magneto or distributor in relation to the TDC or timing marks.
There is a mechanically-based after market device which addresses the problem for only the points actuated model Harley ignitions. It permits the timing marks which normally reside on the fly-wheel, or other pulley which is attached to the crankshaft, to be placed on the camshaft. This, in effect, transfers the timing marks to the opposite side of the engine whereby they are on the same side of the machine as the ignition unit to facilitate adjusting the timing. This device is purely mechanical and the transfer of information to the opposite side of the engine is the sole advantage and benefit of its use. It does not eliminate the trial and error method of setting the ignition timing.
In order to overcome the lack of correlation problem, and to facilitate the accurate setting of the ignition timing in a simpler manner and under true operating conditions rather than by trial and error, it is necessary to provide an engine monitor which does not require major modifications to the motorcycle. However, sensing any type of mark on a motorcycle engine flywheel with an optical-type sensor has several problems. The view port is too small to see much of the flywheel at any time, and oil and dirt quickly obscure the mark. Obviously the inspection port could be opened and the mark repeatedly cleaned, but this is too great of a hindrance and would prevent the utilization of a universal optical sensor for all of the different models of Harley motorcycles.
Likewise, modifying the flywheel of an engine so that an electronic sensor could detect the position of the TDC mark is not really practical. Such a monitor would require an extensive modification that is usually not justifiable. For example, a magnetic/reluctance type pickup that would respond to a TDC mark on a flywheel could be utilized, but there are too many older engines that have beaten up flywheels, and the balancing and drilling which would be required would interfere with reliable operation of the engine. More importantly, however, most owners would not stand the expense or work required to disassemble the engine to add the indicator to the flywheel.
As a result, after much consideration and experimentation, it has been determined that the most practical solution to the problem of setting Harley ignition timing is to obtain the TDC indication from a pickup device mounted on the camshaft, magneto shaft, or distributor shaft in the "nose cone" that houses the Harley ignition unit, either points or electronic, and which is driven from the camshaft. To provide a practical and mechanically simple embodiment of the invention, many options had to be explored. The choices were mechanical (switch or points), magnetic/reluctance, or optical. The use of a magnetic or reluctance-type sensor was considered but that approach was determined to be less desirable because of interference problems with the magnetic ignition sensor and false signals induced by the standard "point type" ignition system.